In recent years, packaging an IC chip on a circuit substrate has used flip chip bonding, so that the distance to connect an inner electrode on the IC chip and an outer electrode on the circuit substrate could be decreased. Flip chip bonding has been carried out in order to improve the noise resistance of the IC as the frequency increases.
A process for manufacturing electrode including forming protrusion electrodes (generally, called bumps) through which the inner electrode of the IC chip is connected to the outer electrode on the circuit substrate on the IC chip. A bump leveling apparatus has been employed conventionally so as to level uniformly a plurality of bumps formed on the electrode of the IC chip so that they are the same height.
A conventional bump leveling method and a bump leveling apparatus are illustrated in FIG. 3A. According to the bump leveling method shown in FIG. 3A, spacers are held between a stage and a leveler depending upon the thickness of the IC chip and the height of the bumps after they are leveled. The distance between the stage and the leveler is maintained to a prescribed distance, so that the bumps are leveled to a prescribed height.
Conventional bump leveling methods and bump apparatuses will be described hereinafter with reference to the drawings.
FIG. 3A is a schematic cross-sectional view showing a construction of a conventional bump leveling apparatus. In FIG. 3A, stage 1 holds an IC chip 2. A spacer 3 allows a leveler 4 to level only the height of bumps 5.
An operation of the bump level apparatus as mentioned above will be described below.
When the bumps 5 are respectively formed with an uneven height, leveling is required so that they have the same height. The leveler 4 is moved downward toward the direction (as shown in FIG. 3A) by a pressing means (not illustrated). When the leveler 4 is held by the spacers 3 provided between the stage 1 and the leveler 4 to retain a prescribed distance from the stage 1, the tip ends 5a of the bumps 5 respectively having uneven height are made flat, as shown in FIG. 3B, and a plurality of bumps 5 are leveled so as to have the same prescribed height.
FIG. 3B shows the form of one bump after a plurality of bumps are leveled. In FIG. 3B, b designates a pedestal diameter, c designates a leveled diameter, d designates the thickness of a pedestal, and e represents the overall height of the bump. IC chip 2 has an inner electrode 6, and pedestal 7 is on top, covering a portion of the electrode. After the bumps are leveled to a prescribed as previously mentioned, the pedestal diameter b, the leveled diameter c, the thickness d of the pedestal, the overall height e of the bump and the misregistration or positional deviation between the inner electrode 6 of the IC chip 2 and the pedestal 7 are all visually examined. This allows for detection of defective bumps 5.
However, problems in the above conventional bump leveling apparatus have occurred that a plurality of spacers 3 need to be maintained, and these spacers 3 must be replaced by new spacers so as to meet the individually measured thickness of the IC chips in order to locate and maintain the accuracy in the overall height of the bumps 5 within a range of .+-.2 .mu.m in the IC chips 2 that have thickness between lots within a range of .+-.10 .mu.m. In this connection, when the height of the bumps 5 is varied to obtain a plurality of bump height, there has arisen a problem that further additional spacers 3 must be retained.
Since it takes a long time for a leveling process, the time required for examining the pedestal thickness d or the overall height e of the bump 5 allows only for a small sampling inspection.